The present invention relates to the field of fluid dynamic bearings, and more specifically to a process for accurately cutting the conical surfaces into a hub to define the hub faces for a conical bearing, so that the motor hub is designed as a single component.
Fluid dynamic bearings have come into increasingly wide-spread use, especially in fields where the stability of the shaft and bearing assembly is of critical importance, such as in the field of disk drives and the like. Ball bearing assemblies have many mechanical problems such as wear, run-out and manufacturing difficulties. Moreover, resistance to operating shock and vibration is poor because of flow damping. Thus, fluid dynamic bearings where in a lubricating fluid such as gas or liquid or air provides a bearing surface between a fixed member of the housing and a relatively rotating member have come into increasingly wide-spread use. Such fluid dynamic bearings spread the bearing surface over a large continuous area in comparison with the ball bearing assembly which comprises a series of point interfaces. This is desirable because the increased bearing surfaces reduce wobble or run-out between the rotating and fixed members. Further, improved shock resistance and readiness is achieved with a fluid dynamic bearing. Also, the use of fluid in the interface area imparts damping effects to the bearing.
An especially desirable design is a conical bearing, as a single bearing or a pair of facing bearings can impart substantial radial and axial stability to a system.
However, due to nominal gaps in a conical fluid bearing on the order of 1 to 3 microns, precise size and positional control must be maintained during component fabrication and assembly. If not done, the assembled components will not have the proper geometric relationships necessary to produce a functional air bearing when the parts rotate at the operating speed.
For purposes of this description, a dual conical fluid bearing spindle includes four basic components. These components are the upper male cone/shaft, the upper female cone, the lower male cone/shaft and the lower female cone. According to the present invention, the upper and lower female cones are integrated into a single part, more specifically the hub. This hub, in designs of a disk drive or the like where the shaft is fixed, may support an external flange for supporting one or more disks for rotation with the hub.
To simplify fabrication of this integral hub piece, the opening between the upper and lower female cones in this hub has sufficient width or radial dimension to allow access to both cones from one side of the hub with the cutting tool. A cutting tool is used which has a width smaller than the opening between the cones. Preferably, the tool has a width which is about equal to or smaller than an angular dimension through this opening which is defined by extending surfaces of the upper and lower female cones. If this limitation is satisfied, both cones can be created with a single machine set up operating from one side of the integrated hub.
Preferably the tool should only move orthogonal or parallel to the cutting tools rotational center axis.
This assembly design and fabrication technique eliminates the tolerance accumulation associated with the assembly of separate upper and lower female cones. Further, since the component manufacturing operation is done on the same machine set-up, there will be no error associated with rechucking the hub between two separate fabrication operations.
Other features and advantages of the present invention will become apparent to a person of skill in the art who studies the following invention disclosure given in association with the following set of drawings.